Armored cable

ABSTRACT

An armored cable for use primarily in underwater geophysical exploration and in offshore oil-drilling operations includes helically wrapped layers of oriented thermoplastic strands surrounding a jacketed core of one or more insulated conductors for providing high-strength armored protection for the core while being resistant to the underwater environment.

United States Patent Inventor Neil Coleman Highland Park, Ill. Appl. No.47,240 Filed June 18, 1970 Patented Jan. I], 1972 Assignee Coleman Cable& Wire Company River Grove, Ill.

ARMORED CABLE 7 Claims. 3 Drawing Figs.

U.S. Cl 174/l20, 174/108,174/1l0PM,174/1l3 R lnt.(.l H0lb7/l8 Fleld ofSearch 174/l0B,

[56] References Cited UNITED STATES PATENTS 2,576,128 11/1951 Lense174/120 3,259,675 7/1966 Bowers [74/113 X 2,604,509 7/1952 Blanchard174/108 FOREIGN PATENTS 338,106 3/1936 Italy l74/l20 PrimaryExaminer-Thomas .I. Kozma Axsislanr Examiner-A. T. Grimley An0rneyFitch,Even, Tabin & Luedeka ABSTRACT: An armored cable for use primarily inunderwater geophysical exploration and in offshore oil-drillingoperations includes helically wrapped layers of oriented thermoplasticstrands surrounding a jacketed core of one or more insulated conductorsfor providing highstrength armored pr0- tection for the core while beingresistant to the underwater environment.

PATENTEDJANI 1 I972 $634607 FIGS STEAlM ARMORED CABLE The presentinvention relates to armored cable useful in geophysical exploration andin offshore oil-drilling operations where the cable is placed and usedunderwater or in a borehole. Reference is hereby made to DisclosureDocument No. 001275 filed Jan. 29, I970.

Armored cable for such use is conventionally constructed by wrappinghelical layers of steel strands about an insulated or jacketed corecomprising one or more insulated conductors. Various steels, such asplow steel, galvanized steel and stainless steel, have been used toprovide armor for such cables. The armor serves the purpose of impartinga relatively high tensile strength to the cable so that the cable doesnot break when extended to a long distance from its secured end or whenlowered to a great depth.

The industry has generally established an unofficial standard forminimum breaking strength for such cables. Thus, it is generallyconsidered that the breaking strength of the cable typically must beequal to or greater than times the weight of 1,000 feet of cable, i.e.,the breaking strength must have a safety factor of 20 times the cablesown weight per 1,000 feet. In examining this standard, it is found thata cable primarily supports its own weight when it extends a longdistance from a fixed terminal. As steelarmored cable has a high tensilestrength, it is commonly employed where the cable is to be suspendedgreat distances underwater. However, the use of steel armor gives riseto a number of disadvantages in such applications. For example, steelhas a high unit weight, and thus the major portion of the breaking ortensile strength is required merely to support the steel armor itself.

Steel armor, moreover, has poor ability to withstand the salt andalkaline conditions present in an underwater environment, and isrelatively inflexible as well as being expensive. Furthermore, it ismagnetic so that it tends to interfere with electrical signals in thecore conductors, and is readily detectable by sonar devices or the likewhich may be objectionable in certain military applications.

Another disadvantage in employing steel armor for electricallyconductive cables is that special preforming equipment is needed to formthe steel strands so that they may be helically wrapped about the cable.It is preferred that the armor strands be wrapped helically withadjacent or contacting turns to prevent damage to the cable core bycompressive forces due to hydrostatic pressure. However, it is difficultand expensive to form steel strands so that they can be helicallywrapped since such strands have or retain a memory of their initialcoiled state so that they generally cannot be wrapped directly from acoil about the cable and must be prebent prior to use. Typical equipmentneeded to preform the steel so that it lays in adjacent turns may coston the order ofone-half million dollars.

Accordingly, a principal object of the present invention is to providean improved armor for underwater cable which provides at least theminimum breaking strength required by the industry for such cable.

Another object of the invention is to provide an improved armored cableable to readily withstand the environment present underwater and whichis relatively flexible and low in cost.

A further object of the invention is to provide improved armor forunderwater cable that may be applied to the cable without necessitatingthe use of special preforming equipment.

These and other objects of the invention are more particularly set forthin the following detailed description and in the accompanying drawingsof which:

FIG. 1 is a perspective view of a portion of an armored cableconstructed in accordance with the present embodiment of the invention,partially broken away to show the layers of armor;

FIG. 2 is an enlarged cross-sectional view taken along the line 2-2 inFIG. 1; and

FIG. 3 is a graphical representation of typical stress-strainrelationships for various materials having potential use as armor forunderwater cables.

Referring to FIG. 1 of the drawing, there is shown a portion of anarmored cable generally indicated by the reference number 10. Thearmored cable 10 is particularly useful in geophysical exploration andin offshore oil-drilling operations where the cable is suspended andused underwater. The cable is armored in order to give it high tensilestrength so that it may be extended great distances from its terminal orat great depths underwater and so that the cable is protected fromexternal hydrostatic pressures. The armored cable 10 is intended, forexample, to be secured at one end to electronic equipment on a ship orother terminal and at its other end to electronic exploration devices orthe like, via suitable connectors (not shown) of conventionalconstruction. Such connectors typically comprise well-known means forrelieving the great tensile or longitudinal stresses on the core,placing essentially the entire loading on the armor, and form no part ofthe present invention.

As shown in FIG. 2, the armored cable 10 has a cable core generallydesignated by the reference numeral 12, that typically includes one ormore coaxial cables l4 and a plurality of single conductors 16. Each ofthe coaxial cables 14 and single conductors l6 desirably containsinsulation 18 thereabout fabricated of a nonconductive plastic materialor the like. A rubber filler 20 or other flexible compositionadvantageously occupies the spaces between the conductors while a binder22 typically surrounds the rubber filler 20 in order to maintain theconductors in proper position within the core 12 during fabrication ofthe cable 10. The binder 22 typically comprises a polyester material,such as Mylar, having one adhesive side engaging the rubber filler 20,although other binders may also be suitable. A jacket 24 encloses theconductors, insulation and filling. It may be of any suitable type andbe fabricated of rubber for protecting the conductors and defining thecore. Preferably, the jacket 24 is resilient so that the core 12 is notunequally compressed due to hydrostatic pressures. Any suitable core 12construction might be employed and these details of core construction donot form a part of the present inventron.

It is a feature of the present structure that the core 12 is sur roundedby plastic armor to give high tensile strength to the cable and toprevent the cable from being compressed by hydrostatic pressures. Thearmor, which is generally designated by the reference numeral 26,comprises a first layer 28 of individual filaments or strands 30 ofhigh-strength plastic material surrounding and protecting the core 12and a second layer 32 of similar strands or filaments 34 surrounding thefirst layer 28 of strands 30. As best seen in FIG. 1, the strands 30constituting the first layer 28 of armor are helic ally or spirallywrapped about the jacket 24. The strands 34 constituting the secondlayer 32 of armor are helically or spirally wrapped about the firstlayer 28, the strands 34, however, having an opposite direction of layto the lay of the strands 30. If the strands 30 are wrapped clockwise,then the strands 34 are desirably wrapped counterclockwise.

Referring to FIG. 2 of the drawing, it may be seen that the strands 30of the first layer 28 are smaller in diameter than the strands 34 of thesecond layer 32. Each strand 34 of the second layer 32 thus correspondswith a strand 30 of the first layer 28. Hence, an equal number ofstrands are present in both the first and second layers 28 and 32. Thepurpose of having an equal number of strands or filaments in each layeris to prevent hydrostatic pressure from compressing the core 12unequally in any given direction. The double wrapping of the strands orfilaments 30 and 34 in combination with disposing the larger strands inthe outer layer prevents distortion of the core 12 by hydrostaticpressures, which would otherwise be likely to produce deleteriouselectrical effects when the cable 10 is in use.

Each of the strands or filaments 30 and 34 is preferably fabricated of aplastic material such as an oriented thermoplastic. The materialemployed, which serves as a substitute for conventionally used steelarmor, must impart a relatively high tensile strength to the cable 10.it should be apparent that oriented thermoplastic materials generallyhave much lower breaking strength than steel or other metals. However,such thermoplastic materials are also relatively lightweight, andrequire less strength to support their own weight. Typically, a cablelike cable 10, but employing steel armor weighs about 480 pounds perL000 feet and has a breaking strength of about 10,320 pounds. Byreplacing the steel with a lightweight thermoplastic material, a cableof the same dimensions will weigh about I40 pounds per 1,000 feet.industry standards require that such cables used in underwaterexploration and oil-drilling operations have a breaking strength equalto or greater than 20 times the weight of 1,000 feet of the cable.Hence, to provide a safe cable employing thermoplastic armor 26 requiresthat the breaking strength of the cable exceed 2,800 pounds, i.e., 140pounds per 1,000 feet multiplied by a safety factor of 20. Anotherrequirement which must be satisfied by cables 10 employing thermoplasticarmor 26 is that the armor be sufficiently resilient that the cable beable to withstand the generally anticipated or forsee able shearingimpacts that a steel-armored cable would be capable of withstanding.Still another requirement which must be met by the orientedthermoplastic material is that the material have a low strain ratio;i.e., it is desirable that the armor 26 not elongate to any substantialdegree. if the armor readily stretches, the entire tensile stress mustthen be absorbed by the core 12, rather than by the armor 26, causingthe core to break and disrupting electrical communication.

Referring to FIG. 3 of the drawings, which is a graphical representationof typical stress-strain values which might be obtained for variousmaterials, it can be seen that oriented polypropylene or compositionsthereof is a preferred material for use as a substitute for steel inproviding armor 26 for un derwater cables 10. Other homopolymers such aspolyethylene and nylon, each break at lower tensile stresses thanoriented polypropylene. Moreover, these other homopolymers each absorb ahigher strain through elasticity than does oriented polypropylene beforereaching their breakpoint. Hence, oriented polypropylene hascharacteristics more closely akin to steel than do the above-mentionedhomopolymers and thus is more suitable for the purpose of the presentinvention.

Oriented polypropylene also exceeds the other standards that have beengenerally established for armored cables. A typical cable 10 employingarmor 26 fabricated of oriented polypropylene monofilaments has beenfound to have a breaking strength of about 3,096 pounds. As the minimumrequired breaking strength for a cable of the given dimensions is about2,800 pounds (as stated above), such cable is suitable for the usescontemplated by the present invention. Even though orientedpolypropylene has only about one-third the tensile strength of steel, italso has only about one-third the weight. Oriented polypropylene is notonly lightweight but is suffi ciently resilient to withstand anyanticipated or forseeable impact tending to shear the cable 10, eventhough the shear strength of the material itself is lower than that ofsteel. Oriented polypropylene is not magnetic and thus does notinterfere with electrical signals and may not be detected by underwaterdetection devices, e.g., sonar devices. Special preforrning equipment isnot needed to wrap strands fabricated of oriented polypropylene aboutthe cores of the cables. Armor 26 fabricated of oriented polypropylenefilament may be applied in helically wrapped layers of opposite lay inorder to prevent hydrostatic pressures from alTecting the cable core 12.

it is contemplated that other thermoplastics, and orientedthermoplastics in particular, having the same or similar characteristicsas oriented polypropylene may alternatively be employed as armor 26 forunderwater cables 10. Oriented polypropylene has a tensile strength ofabout 65,000 p.s.i. and a maximum elongation of about percent at thebreakpoint (a strain ratio of 0.2 in./in.). Unoriented nylon, on theother hand, has a tensile strength of up to about 12,000 p.s.i. and amaximum elongation of up to 300 percent. Polyethylene has even lesstensile strength than nylon and may elongate as much as 800 or 1,000percent. See Modern Plastics Encyclopedia for 1968-69, pages 92-99.Oriented polypropylene does not absorb moisture, has excellent abrasionresistance, is difficult to ignite and upon burning melts to a bead, andhas excellent chemical resistance to most acids, alkalies and salts.Although the cost of oriented polypropylene is somewhat greater perpound than the cost of galvanized steel, the weight of material used inproviding armor 26 for a cable 10 is so much less than the weight ofsteel armor needed that the cost of the cable itself is substantiallyless.

To complete the cable 10 of the illustrated embodiment, a sheathing 36is disposed about the second layer 32 of armor in order to protect thecable from the external environment. The sheathing 36 is desirablyconstructed of hard rubber or somewhat flexible plastic material or anyother suitable waterproof material capable of being extruded, molded orotherwise disposed about a core.

Thus, the present structure provides a lightweight armored cable it]useful primarily in underwater geophysical exploration and in underwateroil-drilling operations or the like. Cable 10 employing armor 26fabricated of oriented polypropylene has a relatively high tensilestrength and meets the typical standards for minimum breaking strengthfor armored cables. Such armor may be wrapped in helical layers toprotect the cable core 12 from compressive hydrostatic forces withoutspecial preforming equipment. Furthermore, the armor is sufiicientlyresilient to withstand normal shearing impacts and is nonmagnetic.

While one specific form of the invention has been shown and described,it should be apparent that various modifications could be made thereinwithout departing from the scope of the invention. The principles of thepresent invention are applicable to cables having various coreconstructions and which require armoring to protect the core.

Various features of the invention are set forth in the following claims.

What is claimed is:

1. In an armored cable having a core which is to be protected, thecombination comprising a first helically wrapped layer of orientedthermoplastic strands surrounding said cable core, and a secondhelically wrapped layer of oriented thermoplastic strands, the lay ofthe strands of said second layer being opposite to the lay of andsurrounding the strands of said first layer, said first and secondlayers providing armoring for the cable core.

2. Armored cable according to claim I wherein said thermoplastic ispolypropylene.

3. Armored cable according to claim 1 wherein each strand has arelatively high tensile strength and a relatively low amount ofelongation at its breaking point.

4. Armored cable according to claim 1 wherein the strands of said secondlayer are greater in diameter than the strands of said first layer, eachstrand of said second layer corresponding to an adjacent strand of saidfirst layer.

5. A cable for use underwater comprising a core and at least one layerof plastic strands surrounding the core to provide armoring for thecore, the strands having a tensile strength of at least about 65,000pounds per square inch and a strain no greater than about 0.2 inches perinch.

6. A cable according to claim 5 wherein the plastic strands are orientedpolypropylene monofilaments.

7. Armored cable comprising:

a. a core having at least one insulated electrical conductor therein anda jacket surrounding said conductor;

b. a first helically wrapped layer of oriented polypropylenemonofilaments surrounding said jacketed core;

c. a second helically wrapped layer of oriented polypropylenemonofilaments, the lay of the monofilaments of said second layer beingopposite to the lay of and surrounding the monofilaments of said firstlayer to provide armoring for said core, the monofilaments of saidsecond layer being greater in diameter than the monofilaments of saidfirst layer; and d. sheathing surrounding said second layer to protectsaid 5 core from the external environment.

I t I l

2. Armored cable according to claim 1 wherein said thermoplastic ispolypropylene.
 3. Armored cable according to claim 1 wherein each strandhas a relatively high tensile strength and a relatively low amount ofelongation at its breaking point.
 4. Armored cable according to claim 1wherein the strands of said second layer are greater in diameter thanthe strands of said first layer, each strand of said second layercorresponding to an adjacent strand of said first layer.
 5. A cable foruse underwater comprising a core and at least one layer of plasticstrands surrounding the core to provide armoring for the core, thestrands having a tensile strength of at least about 65,000 pounds persquare inch and a strain no greater than about 0.2 inches per inch.
 6. Acable according to claim 5 wherein the plastic strands are orientedpolypropylene monofilaments.
 7. Armored cable comprising: a. a corehaving at least one insulated electrical conductor therein and a jacketsurrounding said conductor; b. a first helically wrapped layer oforiented polypropylene monofilaments surrounding said jacketed core; c.a second helically wrapped layer of oriented polypropylenemonofilaments, the lay of the monofilaments of said second layer beingopposite to the lay of and surrounding the monofilaments of said firstlayer to provide armoring for said core, the monofilaments of saidsecond layer being greater in diameter than the monofilaments of saidfirst layer; and d. sheathing surrounding said second layer to protectsaid core from the external environment.